Molded case circuit breaker having an auxiliary contact separating spring

ABSTRACT

A circuit breaker of the molded case type incorporating a spring that accelerates movement of the movable contact to the open circuit position. The same spring augments contact pressure between the movable and stationary contacts in the closed circuit condition of the circuit breaker.

United States Patent Assignee John De Torre;

Henry S. Wingard, both of Albemarle, N.C. 845,275 July 28, 1969 May 25, 1971 Federal Pacific Electric Company lnventors Appl. No Filed Patented MOLDED CASE CIRCUIT BREAKER HAVING AN AUXILIARY CONTACT SEPARATING SPRING 3 Claims, 2 Drawing Figs.

US. Cl 337/67 Int. Cl H0lh 71/16, l-lOlh 71/64, HOlh 75/12 Field ofSearch 335/37,43;

[56] References Cited UNITED STATES PATENTS 2,681,396 6/1954 Cole et al 337/67 2,583,122 1/1952 Rousseau 337/7OX Primary ExaminerG. Harris Assistant Examiner-Dewitt M. Morgan Att0rneysPaul S. Martin and Richard M. Rabkin ABSTRACT: A circuit breaker of the molded case type incorporating a spring that accelerates movement of the movable contact to the open circuit position. The same spring augments contact pressure between the movable and stationary contacts in the closed circuit condition of the circuit breaker.

P EmEnumzSmn v 3581.261

INVENTORS JOHN DETO RRE HENRY 5. WIN GAR D M4. [BM a;

MOLDED CASE CIRCUIT BREAKER HAVING AN AUXILIARY CONTACT SEPARATING SPRING This invention relates to circuit breakers and more particularly to improvements in molded case circuit breakers.

As more and more electricity has been used in homes, offices and factories the capacity of the electric power distribu tion system serving these places has been increased to keep up with the increased demand. The increase in capacity has been accomplished by installation of additional and larger transformers and conductors. With the increased capacity has come an increase in the available short circuit current.

Molded case circuit breakers have been widely employed in the distribution and control of electricity and their popularity continues to increase. In the past the standard circuit breakers which had a short circuit current interrupting capacity of 5,000 ampcreshave been satisfactory. However, in view of the increased short circuit currents available now, and the even greater currents which, it is expected, will be available in the future, it is important that the interrupting capacity of the circuit breakers be increased. Additionally, from an economic viewpoint the improved circuit breakers must be interchangeable with, and if possible externally identical to, the prior units so as to allow continued use of the unchanged panelboards, accessories and the like and to permit improvement or upgrading of existing installations.

Therefore, it is an object of this invention to improve the 7 short circuit current interruption capacity of molded case circuit breakers. It is another object of the invention to improve the interrupting capacity of prior available circuit breakers with minimum exterior changes therein.

The invention is illustrated, in certain of its aspects, as applied to a multipole molded case circuit breaker. Such a circuit breaker is illustrated and described in detail in U.S. Pat.

No. 2,923,795 and that description is incorporated herein by reference.

The nature of the invention and its further objects and features of novelty will be better appreciated from the following detailed description of the illustrative embodiment which is shown in the accompanying drawing forming part of this disclosure. In the drawings:

FIG. I is a side view of an end pole of a three pole circuit breaker with the cover removed and certain parts being shown in fragmentary section. The mechanism is shown in the contacts-closed (closedcircuit) position; and

FIG. 2 is a fragmentary cross section of a portion of the mechanism in FIG. I viewed along the line 2-2 therein.

Referring to the drawings there is shown one end pole of a three-pole circuit breaker of the type described in detail in U.S. Pat. No. 2,923,75. The circuit breaker case has an inner wall 10 that cooperates with an outer wall 12 to form a cavity 14. Cavity l4, and the other like cavities (not shown), each contain a complete circuit breaker mechanism, including a pair of contacts, a contact-operating linkage, an overload release means and a common release means which forms a part of each pole of the three-pole circuit breaker. Common operating means, including externally projecting handle 16, is provided for simultaneous operation of all of the poles. A common trip bar mechanism 18 is operatively connected to all of the poles.

The mechanism of each pole is the same as the mechanism for each of the other poles and only one is shown in detail. Each pole includes a first terminal 20 rigidly'carrying a stationary contact 22. Movable companion contact 24 engages contact 22' when the circuit breaker is closed, movable contact 24 being supported on elongated contact carrying member 26. Contact-carrying member 26 is pivoted near its center on a transverse coil spring 28. The contacts engage and disengage within a well-known type of arc chute 29 that includes metallic arc splitter plates 29a, venting passage 29b and metallic vent screen 29c. Carried on pivot 30 in an insulating bearing (not shown) at the end of contact member 26 remote from contact 24, is an actuator 32 having a bearing 34 which receives a portion of the trip bar mechanism 18. An ambient temperature compensating bimetal 32a has its upper end curved about bearing 34 and its lower end, which constitutes its latched end, is slidably guided by a formed portion of actuator 32 so that the lower tip of bimetal 32 a is projected to a variable extent in dependence on the ambient temperature.

The overcurrent releasable latch 37 includes a current responsive bimetal 38 that is united at one end to the contact arm 26, providing electrical connection and a rigid mechanical connection at this point. The elongated contact member 26 constitutes a conductive support that carries and unites bimetal 38 and the magnetic pole structure 40 of a tripping electromagnet. The pole structure 40 is also united to bimetal 36 and to contact arm 26 by a rivet 26!) that extends integrally, through the bimetal and the pole structure, from contact arm 26. Pole structure 40 is wider than the bimetal 38 and extends all the way acrossthe bimetal except for a cutout portion to accommodate a conductor 42 of flexible conductive braid that is united to the bimetal adjacent its right-hand end as viewed in the drawings. A magnetic armature 44 is positioned on the side of bimetal 38 opposite from pole structure 40 and has lateral pivots 44a retained in notches in the pole structure as shown. Armature 44 is wider than bimetal 38 at the right of pivot 44a and extends into latching engagement with actuator 32. Armature 44 terminates to the left of the pivots 44a. A low profile spring 46 biases the armature counterclockwise about pivots 44a. The novel overcurrent releasable latch 37 is more fully illustrated and described in copending U.S. application Ser. No. 845,274 filed concurrently herewith.

Flexible braid 42 2,647,225one end connected to bimetal 38 and its opposite end is joined to terminal 48, of a form suitable for panelboard plug-in installation as disclosed in U.S. Pat. No. 2,647,225. An electrical circuit may be traced through the circuit breaker from terminal 20 across contacts 22 and 24, into elongated contact member 26, via bimetal 38 and braid 42 to terminal 48. There is no current bypass path bridging bimetal 38 by virtue of the insulated pivot 30 which is more fully disclosed in U.S. Pat. No. 2,647,186.

Transverse coil spring 28, which serves a pivot for contact arm 26, is housed in a pair of cylindrical bosses 10a and I2a that extend inwardly toward one another within the cavity 14. Spring 28 provides contact pressure between the contacts 22 and 24 and permits overtravel of the contact carrying member '26 as more fully explained in U.S. Pat. No. 2,681,396.

A compression spring 50 is interposed between respective projections on contact carrying member 26 and handle 16 biasing both the member and the handle to their open position when the circuit breaker is open. As shown in FIG. I this compression spring provides strong contact-opening bias when the breaker is closed. In the closed configuration of the mechanism shown in FIG. I, actuator 32 is latched by armature 44 and the counterclockwise spring bias applied to contact carrying member 26 is resisted by an overset toggle consisting of trip bar 18 and pivoted handle 16. counterclockwise motion of handle 16 limited by the casing 10. In this configuration, spring 50 provides a limited bias for operating handle I6 in the contact-opening direction.

In part, the speed of opening of the contacts upon occurrence of an overload determines the interrupting capacity of the circuit breaker. The speed of opening is largely dependent upon the force of compression spring 50. An increase in force of spring 50 could produce faster opening. However, spring 50 and pivot spring 28 are in opposition and therefore an increase in force of spring 50 will result in a reduction in contact pressure. An increase of force in spring 50 is therefore not suitable as a way of increasing the speed of opening. A novel solution is provided to the problem of increasing the opening speed of the circuit breaker by the provision of a torsion spring 52 that is positioned about the boss I0a. One end 52a of torsion spring 52 engages a stop 10b on the wall I0 and the other end is formed as a hook 52b for engagement with the contact carrying member 26. Spring 52 is positioned so that it reacts between the casing wall 10 and the contact arm to pivot the contact arm 26 counterclockwise about spring 28 as viewed in FIG. I. Torsion spring 52 acts on the elongated contact carrying member 26 in the same direction as pivot spring 28 when the contacts are closed and therefore spring 52 actually increases the contact pressure. Upon release of the contact carrying member, spring 52 accelerates the movement of contact 24 to the open circuit position.

The toggle comprising handle 16 and trip bar 18 lock the contacts closed, under the control of armature 44 of the overcurrent releasable latch 37. Upon downward deflection of the armature magnetically or by pressure from current responsive bimetal 38, elongated contact carrying member 26 is driven counterclockwise by spring 50 and by spring 52, as actuator 32 swings clockwise about its pivot 30. Springs 50 and 52 are now free to accelerate the separation of the contacts 22, 24. The addition of spring 52 contributes to increased contact pressure and increased speed of opening of the contacts with only a small, barely noticeable to the operator of handle 16, increase in the force required to close the circuit breaker. The molded case circuit breaker illustrated and described above is a three pole, 70 A., 240 v. unit and is fully compatible with presently installed panelboards. Although shown and described as a three-pole breaker it will be readily apparent to those skilled in the art that certain aspects of the invention are equally applicable to circuit breakers having one, two or more poles. Molded case circuit breakers, fabricated according to the teachings of this invention, have been successfully tested at 10,000 A. interrupting capacity.

The resetting and reclosing of the aforedescribed circuit breaker is shown and described in detail in U.S. Pat. No. 2,923,795 and is incorporated herein by reference.

While only one embodiment of the invention has been shown and described in detail it will be readily apparent to those skilled in the art that various changes and modifications may be made herein without departing from the spirit and scope of the invention.

What we claim is:

l. A molded case circuit breaker having a stationary contact, an elongated movable contact member supported on a pivot between its ends, said elongated movable contact member having a contact at one end engageable with and disengageable from said stationary contact, and having an actuator pivoted at its opposite end and having an overcurrent releasable latch normally restraining said actuator, and a pivoted handle and a link connected to said handle forming a toggle for operating said actuator and for thereby operating said elongated movable contact member to close the contacts, said circuit breaker including means for urging said elongated movable contact member in a direction to increase the pressure between the companion contacts when the contacts are engaged and for urging said elongated movable contact member away from said stationary contact when said actuator is released by the overcurrent releasable latch, said last-named means including a torsion spring positioned about said pivot of said elongated movable contact member with one end of the spring bearing against the circuit breaker case and the other end of the spring acting on said elongated movable contact member between the pivot and said actuator.

2. A circuit breaker according to claim 1 wherein said circuit breaker has a case of insulation, said pivot of elongated movable contact member being housed in portions of said case, said torsion spring being positioned about a portion of said pivot housing.

v3. A circuit breaker according to claim 2 wherein said pivot of said elongated movable contact member is a spring, said pivot spring providing the basic pressure between the companion contacts when they are engaged. 

1. A molded case circuit breaker having a stationary contact, an elongated movable contact member supported on a pivot between its ends, said elongated movable contact member having a contact at one end engageable with and disengageable from said stationary contact, and having an actuator pivoted at its oppositE end and having an overcurrent releasable latch normally restraining said actuator, and a pivoted handle and a link connected to said handle forming a toggle for operating said actuator and for thereby operating said elongated movable contact member to close the contacts, said circuit breaker including means for urging said elongated movable contact member in a direction to increase the pressure between the companion contacts when the contacts are engaged and for urging said elongated movable contact member away from said stationary contact when said actuator is released by the overcurrent releasable latch, said last-named means including a torsion spring positioned about said pivot of said elongated movable contact member with one end of the spring bearing against the circuit breaker case and the other end of the spring acting on said elongated movable contact member between the pivot and said actuator.
 2. A circuit breaker according to claim 1 wherein said circuit breaker has a case of insulation, said pivot of elongated movable contact member being housed in portions of said case, said torsion spring being positioned about a portion of said pivot housing.
 3. A circuit breaker according to claim 2 wherein said pivot of said elongated movable contact member is a spring, said pivot spring providing the basic pressure between the companion contacts when they are engaged. 